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Web skærmformat. - Aarhus Universitet

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III. Potensrækker – 4. Taylorpolynomier 309<br />

4.22. Eksponentialrækken konvergerer mod eksponentialfunktionen ☞ [S] 8.7 Taylor ...<br />

Eksempel 2<br />

Tn(x) = 1 + x x2 xn<br />

+ + ... +<br />

1! 2! n!<br />

er afsnits-summen i eksponentialrækken. For hvilke x gælder<br />

For hvilke x gælder<br />

For alle x ! THI:<br />

Tn(x) → e x for n → ∞?<br />

Rn(x) → 0 for n → ∞?<br />

4.23. Eksponentialrækken ☞ [S] 8.7 Taylor and Maclaurin series<br />

tag et d ≥ x. I intervallet [−d,d] er<br />

så restledsvurderingen giver<br />

f (n+1) (x) = e x ≤ e d<br />

|Rn(x)| ≤<br />

for |x| ≤ d. Men |x|n+1<br />

(n+1)! → 0 for n → ∞.<br />

Altså Rn(x) → 0 for n → ∞<br />

Altså Tn(x) → f(x) = e x for n → ∞.<br />

e d<br />

(n + 1)! |x|n+1

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